Method of manufacturing silicon carbide substrate

ABSTRACT

A method of manufacturing a silicon carbide substrate has the following steps. A silicon carbide source material is partially sublimated. After partially sublimating the silicon carbide source material, a seed substrate having a main surface is placed in a growth container. By sublimating the remainder of the silicon carbide source material in the growth container, a silicon carbide crystal grows on the main surface of the seed substrate. In this way, an increase of dislocations in the main surface of the seed substrate can be suppressed, thereby providing a method of manufacturing a silicon carbide substrate having few dislocations.

TITLE OF INVENTION

Method of Manufacturing Silicon Carbide Substrate

TECHNICAL FIELD

The present invention relates to a method of manufacturing a siliconcarbide substrate, more particularly, to a method of manufacturing asilicon carbide substrate having few dislocations.

BACKGROUND ART

In recent years, a silicon carbide substrate has begun to be adopted formanufacturing of a semiconductor device. Silicon carbide has a widerband gap than that of silicon. Hence, a semiconductor device using asilicon carbide substrate has advantages such as a high breakdownvoltage, a low on-resistance and a less deteriorated property under ahigh temperature condition.

A silicon carbide single crystal can be manufactured by asublimation-recrystallization method, for example. For example, JapanesePatent Laying-Open No. 2007-284306 (Patent Document 1) describes amethod of manufacturing a silicon carbide single crystal with a specificsurface area of a source material silicon carbide powder being set to benot less than 0.001 m²/g and not more than 0.05 m²/g. Japanese PatentLaying-Open No. 2009-234802 (Patent Document 2) describes a method ofmanufacturing a silicon carbide single crystal by performing apretreatment to maintain, for a predetermined time, a crucible under areduced-pressure atmosphere at a temperature equal to or more than atemperature at which the silicon carbide source material does notsublime and then sublimating the silicon carbide source material underan inert gas atmosphere.

CITATION LIST Patent Document

PTD 1: Japanese Patent Laying-Open No. 2007-284306

PTD 2: Japanese Patent Laying-Open No. 2009-234802

SUMMARY OF INVENTION Technical Problem

However, in manufacturing the silicon carbide crystal by each of themethods described above, it is impossible to sufficiently suppress anincrease of dislocations in a main surface of a seed substrate and it isdifficult to obtain a silicon carbide substrate having few dislocations.

The present invention has been made to solve the foregoing problem, andhas its object to provide a method of manufacturing a silicon carbidesubstrate having few dislocations by suppressing an increase ofdislocations in a main surface of a seed substrate.

Solution to Problem

The present inventors have diligently studied a reason for the increaseof dislocations in the main surface of the seed substrate in the case ofmanufacturing a silicon carbide single crystal by the sublimation methodand accordingly have conceived the present invention based on thefollowing findings. In order to grow a high-quality silicon carbidesingle crystal by the sublimation method, it is important to control asublimation gas. The sublimation gas can be produced by heating andsublimating a silicon carbide powder as a source material. Althoughcomposition and vapor pressure of the sublimation gas do not depend on aparticle size of the silicon carbide source material powder in the idealcase, they depend on the particle size in the actual case. Therefore, itis important to optimize the particle size and/or specific surface areaof the silicon carbide source material powder. However, even though theparticle size and/or specific surface area of the silicon carbide sourcematerial powder are controlled, the silicon carbide source materialpowder is partially crushed to generate fine particles or a damagedlayer is formed in the silicon carbide source material powder duringhandling of the silicon carbide source material powder. The existence ofthe fine powder and damaged layer causes an increase of dislocations inthe silicon carbide crystal at an initial stage of the crystal growth.

As a result of examining a method of removing the fine powder in thesilicon carbide source material powder, it has been conceived that it iseffective to sublimate and accordingly remove the fine powder or thedamaged layer before growing the silicon carbide crystal on the mainsurface of the seed substrate. A fine powder having a small particlesize has a small radius of curvature in its form. Therefore, surfaceenergy becomes large, so that it is likely to sublime. Even when thepowder has a large particle size, the damaged layer in the surface islikely to sublime. In view of this, by partially sublimating the siliconcarbide source material before placing the seed substrate in the growthcontainer, the fine powder and damaged layer, which would have caused anincrease of dislocations, can be preferentially removed.

Thus, a method of manufacturing a silicon carbide substrate in thepresent invention includes the following steps. A silicon carbide sourcematerial is partially sublimated. A seed substrate having a main surfaceis placed in a growth container after partially sublimating the siliconcarbide source material. A silicon carbide crystal is grown on the mainsurface of the seed substrate by sublimating a remainder of the siliconcarbide source material in the growth container.

According to the method of manufacturing the silicon carbide substratein accordance with the present invention, the silicon carbide sourcematerial is partially sublimated and then the remainder of the siliconcarbide source material is sublimated, thereby growing the siliconcarbide single crystal on the main surface of the seed substrate. Inthis way, the silicon carbide single crystal can be grown on the mainsurface of the seed substrate after sublimating and removingpreferentially the fine powder or damaged layer, which would have causedan increase of dislocations at the initial stage of the crystal growth.Moreover, since the seed substrate is placed in the growth containerafter partially sublimating the silicon carbide source material, theseed substrate can be prevented from being contaminated by thesublimated fine powder and damaged layer. As a result, a silicon carbidesubstrate having few dislocations can be obtained.

Preferably in the method of manufacturing the silicon carbide substrate,the step of growing the silicon carbide crystal is performed withoutproviding a mechanical process to the remainder of the silicon carbidesource material, after the step of partially sublimating the siliconcarbide source material. Accordingly, the fine powder and damaged layercan be prevented from being generated in the remainder of the siliconcarbide source material.

Preferably in the method of manufacturing the silicon carbide substrate,a value obtained by subtracting a second dislocation density just belowthe main surface of the seed substrate from a first dislocation densityjust above the main surface of the seed substrate is not more than 1×10³cm⁻². In this way, a silicon carbide substrate having few dislocationscan be effectively obtained.

Preferably, the method of manufacturing the silicon carbide substratefurther includes the step of reducing a silicon carbide fine powder inthe silicon carbide source material before partially sublimating thesilicon carbide source material. In this way, a silicon carbidesubstrate having few dislocations can be more effectively obtained.

Preferably in the method of manufacturing the silicon carbide substrate,the step of reducing the silicon carbide fine powder is performed byimmersing the silicon carbide source material in a liquid and removingthe silicon carbide fine powder floating on a surface of the liquid. Inthis way, with such a simple method, the silicon carbide fine powder canbe removed from the silicon carbide source material.

Advantageous Effects of Invention

According to the present invention, the silicon carbide crystal havingfew dislocations can be obtained by suppressing the increase ofdislocations in the main surface of the seed substrate.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a flowchart schematically showing a method of manufacturing asilicon carbide substrate in accordance with an embodiment of thepresent invention.

FIG. 2 is a schematic cross sectional view schematically showing a firststep of the method of manufacturing the silicon carbide substrate inaccordance with the embodiment of the present invention.

FIG. 3 is a schematic cross sectional view schematically showing asecond step of the method of manufacturing the silicon carbide substratein accordance with the embodiment of the present invention.

FIG. 4 is a schematic cross sectional view schematically showing a thirdstep of the method of manufacturing the silicon carbide substrate inaccordance with the embodiment of the present invention.

FIG. 5 is a schematic cross sectional view schematically showing onestep of the method of manufacturing the silicon carbide substrate inaccordance with the embodiment of the present invention.

FIG. 6 illustrates a method of measuring an amount of increase ofdislocations in a main surface of a seed substrate.

FIG. 7 illustrates the method of measuring the amount of increase ofdislocations in the main surface of the seed substrate.

FIG. 8 illustrates the method of measuring the amount of increase ofdislocations in the main surface of the seed substrate.

DESCRIPTION OF EMBODIMENTS

The following describes embodiments of the present invention withreference to figures. It should be noted that in the below-mentionedfigures, the same or corresponding portions are given the same referencecharacters and are not described repeatedly. Further, regardingcrystallographical indications in the present specification, anindividual orientation is represented by H, a group orientation isrepresented by <>, and an individual plane is represented by Q, and agroup plane is represented by {}. In addition, a negative index issupposed to be crystallographically indicated by putting “−” (bar) abovea numeral, but is indicated by putting the negative sign before thenumeral in the present specification. For description of an angle, asystem in which an omnidirectional angle is 360° is employed.

Referring to FIG. 3, a structure of an apparatus for manufacturing asilicon carbide substrate in accordance with the present embodiment willbe described.

Referring to FIG. 3, the apparatus for manufacturing the silicon carbidesubstrate in accordance with the present embodiment mainly includes agrowth container 10 and a heat insulator 4. Growth container 10 is acrucible made of, for example, purified graphite, and includes a seedsubstrate retaining portion 3 and a source material accommodatingportion 7. Seed substrate retaining portion 3 retains a seed substratemade of single-crystal silicon carbide, for example. Source materialaccommodating portion 7 accommodates silicon carbide source material 8made of polycrystal silicon carbide, for example.

Heat insulator 4 is made of, for example, felt and insulates growthcontainer 10 from heat externally. Heat insulator 4 is formed tosurround the external wall surface of growth container 10, for example.Heat insulator 4 is provided with a plurality of through holes 2 a, 2 b.Seed substrate retaining portion 3 has an upper surface, a part of whichis exposed through a through hole 2 a formed in heat insulator 4. On theother hand, source material accommodating portion 7 has a bottomsurface, a part of which is exposed through a through hole 2 b formed inheat insulator 4.

Referring to FIG. 1 to FIG. 5, the following describes a method ofmanufacturing the silicon carbide substrate in accordance with thepresent embodiment.

First, a seed substrate 1 made of, for example, a silicon carbide singlecrystal is prepared. Seed substrate 1 has a polytype of 4H, for example.Seed substrate 1 has a diameter of, for example, 6 inches, preferably, 4inches (100 mm) or more. Seed substrate 1 has a main surface 1Acorresponding to a (0001) C plane off by about 4°, for example. Athreading dislocation density in main surface 1A of seed substrate 1 isabout 1000 cm⁻², for example. Seed substrate 1 has its surfaces polishedthrough CMP (Chemical Mechanical Polishing). Seed substrate 1 has awarpage of less than 10 μm, for example.

In the present embodiment, main surface 1A of seed substrate 1 is etchedunder a silicon gas atmosphere. Specifically, a crucible made ofgraphite for etching is placed in a heating furnace. After evacuatingthe heating furnace, the heating furnace is filled with argon (Ar) atabout 70 kPa, for example. Seed substrate 1 is placed at an upperportion in the crucible for etching. In the crucible, silicon is placedand no silicon carbide source material powder is placed. It should benoted that the silicon placed in the crucible is high-purity silicon(9N), for example. The upper portion of the crucible for etching ismaintained at about 1700° C. and the lower portion thereof is maintainedat about 1600° C. for about 1 hour. Accordingly, main surface 1A of seedsubstrate 1 made of single-crystal silicon carbide is etched under thesilicon gas atmosphere. It is etched by a thickness of not less than 0.2μm and not more than 0.5 μm, for example. With this etching, a damagedlayer (a layer including defects and dislocations) is removed from mainsurface 1A of seed substrate 1.

Next, a silicon carbide source material 8 is prepared. Silicon carbidesource material 8 is formed of a polycrystal silicon carbide powder, forexample. For silicon carbide source material 8, a high-purity a-siliconcarbide powder can be used, for example. The silicon carbide powder hasan average particle size of, for example, about 100 μm and has a maximumparticle size of about 200 μm. Further, the silicon carbide powderincludes a silicon carbide fine powder of about 2 μm to 3μm, forexample. The fine powder in the present embodiment is, for example, asilicon carbide powder having a particle size of 30 μm or less,preferably, a silicon carbide powder having a particle size of 10 μm orless.

Next, the step of removing the fine powder in the silicon carbide sourcematerial is performed. Specifically, referring to FIG. 5, siliconcarbide source material 8 is cleaned using a liquid 13. As liquid 13,hydrochloric acid having a concentration of 35% can be used, forexample. Silicon carbide has a specific gravity larger than that of thehydrochloric acid and therefore basically sinks in the hydrochloricacid. However, fine powder 8 a of silicon carbide floats on the liquidsurface due to surface tension of the hydrochloric acid (liquid). Byscooping only the floating fine powder 8 a from the liquid surface, finepowder 8 a is separated and removed from silicon carbide source material8. In this way, silicon carbide fine powder 8 a in silicon carbidesource material 8 is reduced. It should be noted that the step ofreducing fine powder 8 a in silicon carbide source material 8 ispreferably performed before the below-described silicon carbide sourcematerial partial sublimating step.

Next, silicon carbide source material 8 is cleaned using aqua regia (aliquid obtained by mixing the hydrochloric acid having a concentrationof 35% with sulfuric acid having a concentration of 60% at a volumeratio of 3:1). Then, silicon carbide source material 8 is cleaned usingpure water. Preferably, silicon carbide source material 8 is cleaned fora plurality of times using the hydrochloric acid, the aqua regia, andthe pure water. Preferably, the cleaning is repeated until fine powder 8a having a size visible to the eye ceases to exist. As described above,silicon carbide source material 8 is immersed in the acid liquid such ashydrochloric acid and aqua regia, thereby removing fine powder 8 a madeof silicon carbide and floating on the surface of the liquid. Then,silicon carbide source material 8 is taken out of beaker 12 and isdried.

Next, a silicon carbide source material placing step (S10: FIG. 1) isperformed. Referring to FIG. 2, in the silicon carbide source materialplacing step, silicon carbide source material 8 is accommodated insource material accommodating portion 7 of growth container 10. It ispreferable to use a silicon carbide source material from which the finepowder made of silicon carbide has been removed through the cleaningstep.

Next, a silicon carbide source material partial sublimating step (S20:FIG. 1) is performed. Specifically, referring to FIG. 2, growthcontainer 10 having silicon carbide source material 8 placed therein isplaced in a high-frequency heating furnace. After evacuating thehigh-frequency heating furnace, a pressure is maintained at, forexample, 800 kPa while introducing an inert gas such as argon gas. Whilemaintaining the pressure at, for example, 800 kPa, the temperature ofthe lower portion of growth container 10 (i.e., the bottom portion ofsource material accommodating portion 7) is set at, for example, 2400°C. and the temperature of the upper portion of growth container 10(i.e., seed substrate retaining portion 3) is set at 2200° C., forexample. Then, the pressure of the high-frequency heating furnace isreduced to, for example, 4 kPa and is retained for about 24 hours. Inthis way, the fine powder in silicon carbide source material 8 and thedamaged layer of silicon carbide source material 8 are sublimatedpreferentially. Then, the pressure in the high-frequency heating furnaceis brought back to, for example, 800 kPa, and growth container 10 isthereafter cooled to a room temperature. It should be noted that in thesilicon carbide source material partial sublimating step, seed substrate1 is not placed in seed substrate retaining portion 3 of growthcontainer 10.

It should be noted that when observing seed substrate retaining portion3 after the silicon carbide source material partial sublimation step, amultiplicity of silicon carbide crystal nuclei each having a size ofseveral millimeters are interspersed in seed substrate retaining portion3. In other words, if the silicon carbide source material is partiallysublimated with seed substrate 1 being retained by seed substrateretaining portion 3, the crystal nuclei are adhered to seed substrate 1.Therefore, in the silicon carbide source material partial sublimatingstep, it is preferable not to place the seed substrate.

Moreover, silicon carbide source material 8 remaining in source materialaccommodating portion 7 after the silicon carbide source materialpartial sublimating step is entirely merged into a pumice-like form (inthe form of a porous sintered body). If silicon carbide source material8 in the form of sintered body is subjected to a mechanical process suchas pulverization, fine powder is generated again. Hence, after partiallysublimating silicon carbide source material 8, it is preferable toperform silicon carbide crystal growth described below without providinga mechanical process to the remainder of silicon carbide source material8.

Moreover, the silicon carbide source material partial sublimating stepmay be performed in vacuum and may be performed involving an impurityhaving no adverse effect on the silicon carbide single crystal growth.For example, by including hydrogen or halogen in the atmospheric gas,fine powder 8 a may be facilitated to become non-existent. Sincehydrogen and halogen function as an etching gas, fine powder 8 a isfacilitated to become non-existent due to chemical etching in additionto the sublimation of the silicon carbide source material.

Next, the seed substrate placing step (S30: FIG. 1) is performed.Specifically, referring to FIG. 3, seed substrate retaining portion 3 ofgrowth container 10 used in the silicon carbide source material partialsublimating step is replaced with another seed substrate retainingportion 3 having seed substrate 1 placed thereon. As described above,after partially sublimating silicon carbide source material 8, seedsubstrate 1 having main surface 1A is placed in growth container 10.

Next, the silicon carbide crystal growth step (S40: FIG. 1) isperformed. Specifically, referring to FIG. 3, growth container 10 havingseed substrate 1 and silicon carbide source material 8 placed therein isplaced in the high-frequency heating furnace again. Then, thehigh-frequency heating furnace is evacuated and the pressure ismaintained at, for example, 800 kPa while introducing a mixed gas ofargon gas and nitrogen gas (1%). While maintaining the pressure at, forexample, 800 kPa, the temperature of the lower portion of growthcontainer 10 (i.e., the bottom portion of source material accommodatingportion 7) is set at, for example, 2400° C. and the temperature of theupper portion of growth container 10 (i.e., seed substrate retainingportion 3) is set at 2200° C., for example. Then, the pressure isreduced for 1 hour until the pressure in the high-frequency heatingfurnace becomes, for example, 2 kPa. Referring to FIG. 4, siliconcarbide source material 8 is sublimated and is recrystallized on mainsurface 1A of seed substrate 1, whereby silicon carbide single crystal11 grows on main surface 1A of seed substrate 1. After growing siliconcarbide single crystal 11 for, for example, 100 hours, the pressure inthe high-frequency heating furnace is set at, for example, 800 kPaagain. Then, the temperature of growth container 10 is brought back tothe room temperature. By sublimating the remainder of silicon carbidesource material 8 as described above, silicon carbide single crystal 11is grown on main surface 1A of seed substrate 1.

It is preferable that after partially sublimating the silicon carbidesource material, silicon carbide single crystal 11 is grown withoutproviding a mechanical process to the remainder of the silicon carbidesource material. For example, when the silicon carbide source materialis subjected to a mechanical process such as pulverization, fine powderis generated in the silicon carbide source material. Preferably, noimpact is given to silicon carbide source material 8 after partiallysublimating silicon carbide source material 8 and before growing siliconcarbide single crystal 11,

Next, silicon carbide single crystal 11 is taken out of growth container10. Then, silicon carbide single crystal 11 is sliced using, forexample, a wire saw, thereby obtaining a silicon carbide substrate.

It should be noted that, in the present embodiment, the method ofpartially sublimating silicon carbide source material 8 in growthcontainer 10 has been illustrated, but the present invention is notlimited to this method. For example, silicon carbide source material 8may be partially sublimated in a container different from growthcontainer 10, the remaining silicon carbide source material 8 may besubjected to no mechanical process, the remaining silicon carbide sourcematerial 8 may be moved to growth container 10, and then the remainingsilicon carbide source material 8 may be sublimated, thereby growingsilicon carbide single crystal 11 on main surface 1A of seed substrate1.

The following describes function and effect of the method ofmanufacturing the silicon carbide substrate in accordance with thepresent embodiment.

According to the method of manufacturing the silicon carbide substratein accordance with the present embodiment, silicon carbide sourcematerial 8 is partially sublimated and then the remainder of siliconcarbide source material 8 is sublimated, thereby growing silicon carbidesingle crystal 11 on main surface 1A of seed substrate 1. In this way,silicon carbide single crystal 11 can be grown on main surface 1A ofseed substrate 1 after sublimating and removing preferentially the finepowder or damaged layer, which would have caused an increase ofdislocations at the initial stage of the crystal growth. Moreover, sinceseed substrate 1 is placed in growth container 10 after partiallysublimating silicon carbide source material 8, seed substrate 1 can beprevented from being contaminated by the sublimated fine powder anddamaged layer. As a result, a silicon carbide substrate having fewdislocations can be obtained.

Moreover, according to the method of manufacturing the silicon carbidesubstrate in accordance with the present embodiment, the step of growingsilicon carbide single crystal 11 is performed without providing amechanical process to the remainder of silicon carbide source material8, after the step of partially sublimating silicon carbide sourcematerial 8. In this way, the fine powder and the damaged layer can beprevented from being generated in the remainder of silicon carbidesource material 8.

Further, according to the method of manufacturing the silicon carbidesubstrate in accordance with the present embodiment, a value obtained bysubtracting a second dislocation density just below main surface 1A ofseed substrate 1 from a first dislocation density just above mainsurface 1A of seed substrate 1 is not more than 1×10³ cm⁻². In this way,a silicon carbide substrate having few dislocations can be effectivelyobtained.

Moreover, the method of manufacturing the silicon carbide substrate inaccordance with the present embodiment further includes the step ofreducing a silicon carbide fine powder 8 a in silicon carbide sourcematerial 8 before partially sublimating silicon carbide source material8. In this way, a silicon carbide substrate having few dislocations canbe more effectively obtained.

Further, according to the method of manufacturing the silicon carbidesubstrate in accordance with the present embodiment, the step ofreducing silicon carbide fine powder 8 a is performed by immersingsilicon carbide source material 8 in hydrochloric acid and aqua regiaand removing silicon carbide fine powder 8 a floating on a surface ofthe hydrochloric acid and aqua regia. In this way, with such a simplemethod, silicon carbide fine powder 8 a can be removed from siliconcarbide source material 8.

EXAMPLE

In the present example, silicon carbide single crystals were grown usingthree types of methods illustrated below so as to examine a rate ofincrease in the dislocation density in main surface 1A of each seedsubstrate 1. The silicon carbide crystals of the present invention'sexample, a comparative example 1, and a comparative example 2 werefabricated using the same method as the method described in theembodiment except differences described below. The method ofmanufacturing silicon carbide single crystal 11 in comparative example 1was different from the manufacturing method of the present invention'sexample in that a commercially available silicon carbide source material8 was used without any modification and the method in comparativeexample 1 did not include the silicon carbide source material partialsublimating step and did not include the step of removing the finepowder through acid cleaning before the sublimation, and the method ofmanufacturing silicon carbide single crystal 11 in comparative example 1is the same as the manufacturing method of the present invention'sexample in the other points. The method of manufacturing silicon carbidesingle crystal 11 in comparative example 2 was different from themanufacturing method of the present invention's example in that themethod of manufacturing silicon carbide single crystal 11 in comparativeexample 2 did not include the silicon carbide source material partialsublimating step, and was the same as the manufacturing method of thepresent invention's example in the other points.

The following describes a method of determining a rate of increase inthe dislocation density in main surface 1A of seed substrate 1. First,referring to FIG. 6, silicon carbide single crystal 11 grown on mainsurface 1A of seed substrate 1 was taken out and was sliced along aplane parallel to main surface 1A of seed substrate 1, thereby preparinga substrate having seed substrate 1 and silicon carbide single crystal11. Next, referring to FIG. 7, the substrate was started to be polishedfrom the silicon plane 1B side so as to polish seed substrate 1 suchthat the thickness of seed substrate 1 from main surface 1A (i.e.,growth interface) became thickness T1. Thickness T1 of the remainingseed substrate 1 was about 100 μm. A threading dislocation density insurface 1C of seed substrate 1 was evaluated using KOH (potassiumhydroxide) etching.

Thereafter, referring to FIG. 8, the substrate was further polished topolish the whole of seed substrate 1, and then silicon carbide singlecrystal 11 was polished only by a thickness T2. Thickness T2 by whichsilicon carbide single crystal 11 was polished was about 100 μm.Accordingly, there was obtained silicon carbide single crystal 11 havingsurface 11A exposed. A threading dislocation density in surface 11A ofsilicon carbide single crystal 11 was evaluated using KOH etching.

The threading dislocation density was measured at 177 locations insurface 1C and surface 11A (at a pitch of 10 mm). Each measurement areawas 2 mm×2 mm. The rate of increase in the threading dislocation densitywas represented by a value obtained by subtracting the threadingdislocation density (second dislocation density) in surface 1C of seedsubstrate 1 (i.e., just below main surface 1A) from the threadingdislocation density (first dislocation density) in surface 11A ofsilicon carbide single crystal 11 (i.e., just above main surface 1A). Itshould be noted that a positioning marking was provided through laserprocessing for the purpose of measurement at corresponding positionsjust above and just below the main surface in the directionperpendicular to main surface 1A.

TABLE 1 Source Material Partial Rate of Increase in Sublimation beforeAcid Threading Dislocation Crystal Growth Cleaning Density The PresentInvention's Performed Performed   1 × 10³ cm⁻² or less Example  Comparative Example 1 Not Performed Performed 3.7 × 10³ cm⁻² ComparativeExample 2 Not Performed Not Performed 8.5 × 10⁴ cm⁻²

Referring to Table 1, the following describes a result regarding therate of increase in the threading dislocation density. The rate ofincrease in the threading dislocation density in the present invention'sexample was +cm⁻² (+3 in the measurement area) at maximum and was −175cm⁻² at minimum (−7 in the measurement area), and the average was −30cm⁻² (−1.2 in the measurement area). Here, “+” indicates that thethreading dislocation density was increased and “−” indicates that thethreading dislocation density was decreased. In addition, although it isdifficult to evaluate the increase/decrease in the dislocation densityprecisely because there are possibilities of movement of dislocationpositions and displacement of positions just above and just below themain surface in the direction perpendicular to main surface 1A, the rateof increase in the threading dislocation density in the presentinvention's example was at least 1×10³ cm⁻² or less. It should be notedthat in the present invention's example, the threading dislocationdensity was slightly reduced. This is presumably because dislocationshaving opposite Burgers vectors were merged with each other at the earlystage of the growth and accordingly ceased to exist. Further, the rateof increase in the threading dislocation density in comparative example1 was about 3.7×10³ cm⁻², and the rate of increase in the threadingdislocation density in comparative example 2 was about 8.5×10⁴ cm⁻².

From the result above, it was confirmed that a silicon carbide crystalhaving a low dislocation density is obtained by partially sublimatingthe silicon carbide source material before the crystal growth of siliconcarbide. Moreover, it was confirmed that the silicon carbide crystalhaving a smaller dislocation density can be obtained by removing siliconcarbide fine particles through the acid cleaning for the silicon carbidesource material before partially sublimating the silicon carbide sourcematerial.

The embodiments and examples disclosed herein are illustrative andnon-restrictive in any respect. The scope of the present invention isdefined by the terms of the claims, rather than the embodimentsdescribed above, and is intended to include any modifications within thescope and meaning equivalent to the terms of the claims.

REFERENCE SIGNS LIST

1: seed substrate; 1A: main surface; 1B: silicon plane; 1C: surface; 2a, 2 b: through hole; 3: seed substrate retaining portion; 4: heatinsulator; 7: source material accommodating portion; 8: silicon carbidesource material; 8 a: fine particle; 10: growth container; 11: siliconcarbide single crystal; 11A: surface; 12: beaker; 13: liquid.

1. A method of manufacturing a silicon carbide substrate, comprising thesteps of: reducing a silicon carbide fine powder in a silicon carbidesource material by immersing said silicon carbide source material in anacid and removing said silicon carbide fine powder floating on a surfaceof said acid; partially sublimating said silicon carbide source materialafter the step of reducing a silicon carbide fine powder; placing a seedsubstrate having a main surface in a growth container after the step ofpartially sublimating said silicon carbide source material; and growinga silicon carbide crystal on said main surface of said seed substrate bysublimating a remainder of said silicon carbide source material in saidgrowth container.
 2. The method of manufacturing a silicon carbidesubstrate according to claim 1, wherein the step of growing said siliconcarbide crystal is performed without providing a mechanical process tothe remainder of said silicon carbide source material, after the step ofpartially sublimating said silicon carbide source material.
 3. Themethod of manufacturing a silicon carbide substrate according to claim1, wherein a value obtained by subtracting a second dislocation densityjust below said main surface of said seed substrate from a firstdislocation density just above said main surface of said seed substrateis not more than 1×10³ cm⁻².
 4. The method of manufacturing a siliconcarbide substrate according to claim 1, wherein said acid includes ahydrochloric acid and an aqua regia.
 5. (canceled)